As we changed the meaning of unstable between the old vocabulary and the new
one, we can't reuse the unstable method name at the risk of breaking
extensions calling unstable and getting a wrong result.
Instead rename troubled into isunstable so extensions will continue to work.
The renaming is done according to
https://www.mercurial-scm.org/wiki/CEDVocabulary.
Please send a follow-up. This is too far from the tip to amend.